This invention relates to fuel cell power plants and, in particular, to practices for achieving rapid start-up time of such power plants.
In fuel cell power plants, and, in particular, in power plants designed to be transportable, it is desirable that the power plant have a relatively rapid start-up. In present state-of-the-art power plants the factor which limits start-up time is the time it takes to preheat the fuel cell stack.
In these state-of-the-art systems, one way of preheating the fuel cell stack is to provide an external burner in the path of the air provided to replenish the air in the stack cooling/heating loop. During start-up, fuel provided by the stack reformer is burned in the burner with air which is drawn to the burner during the start-up phase of operation. The resultant heated air is then introduced into the stack through the cooling/heating loop where it heats the air being recirculated. This introduction of the heated air occurs upstream of a blower which is situated in the loop and used for forcing recirculation.
The aforesaid preheating arrangement, while usable, has certain drawbacks which, if overcome, would quicken start-up, as well as provide other system benefits. More particularly, with the described heating arrangement, the stack preheating temperature is limited by the temperature constraints of the blower material and the blower electronics since these are subjected to and, thus, must be able to withstand the temperature of the heated air. Typically, blowers for this application are designed to accommodate temperatures of below 500.degree. F., thereby limiting the temperature of the heated air to this level. Higher temperatures, however, would enable faster start-up, but with the existing system could be realized only at significant expense of increasing the temperature characteristcs of the blowers used.
The inability to increase start-up time with the above preheating arrangement also leads to greater thermal and electrical requirements for the power plant. This is due to the fact that about one-third of the air in the cooling/heating loop is exhausted, so that longer start-up times result in increased amount of exhausted air as well as increased amounts of flue from the stack reformer, both of which constitute thermal energy loss.
Other drawbacks of the preheating arrangement involve the need to insulate the burner in order to avoid thermal signature and the need to use higher temperature burner materials capable of withstanding wall temperatures in the range of about 2500.degree. F. The external burner is also noisy as a result of flame hydrodynamics.
It is therefore a primary object of the present invention to provide an apparatus for fuel cell power plant start-up which substantially avoids the drawbacks of the abovedescribed arrangement.
It is a further object of the present invention to provide an apparatus for fuel cell power plant start-up which enables a more rapid start-up.
It is yet a further object of the present invention to provide an apparatus for fuel cell power plant start-up which decouples start-up time from blower characteristcs, and which also suppresses burner thermal signature, dampens blower noise and reduces energy consumption during start-up.